1. Field of the Invention
The present invention relates to an apparatus for spectroanalysis by using a light transmitted from an object under test through an optical fiber placed in a radiation environment.
2. Related Background Art
An optical fiber has a property that when it is irradiated with a radiation, a transmissibility thereof is gradually lost and eventually it reaches a level which does not enable spectroanalysis. In JP-A-63-309707, it has been proposed to prolong a life of the spectroanalyzer by utilizing a so-called photo-bleaching effect in which a radiation induction loss is recovered by a strong light. FIG. 1 shows an example of the spectroanalyzer which utilizes the photo-bleaching effect.
As shown in FIG. 1, the prior art spectroanalyzer comprises a sample cell 1 which is an object to be tested, micro-lenses 2 and 6, an optical fiber 5, a photo-bleach light source 14 and a spectrometer 16.
A light (measurement light) emitted from the sample cell 1 is condensed by a micro-lens 2 and directed to the spectrometer 16 through the optical fiber 5, the micro-lens 6 and a wave combiner 9. Since a portion of the optical fiber 5 which is inside a shield wall 4, that is, which is exposed to the sample cell 1 is in a radiation environment, a transmissibility thereof gradually falls if the optical fiber 5 is left as it is and finally the spectroanalysis is disabled. A structural defect of a molecule level occurs in the optical fiber by the irradiation of the radiation and the light is absorbed thereby so that a light transmission loss of the optical fiber increases and the transmissibility is deteriorated. By irradiating a photo-bleach light to the optical fiber 5 by using the photo-bleach light source 14 and the wave combiner 9, the structural defect of the molecule level is extinguished and the progress of the deterioration of the transmissibility is delayed.
However, even by the irradiation of the photo-bleach light, the transmissibility is still deteriorated gradually, and the light transmission loss increases and the light intensity passed through the optical fiber 5 decreases. Accordingly, the spectroanalyzer is not sufficient when reproductability is required.